Field of the Disclosure
Embodiments of the present disclosure relate to the art of a drive unit having an engine and a motor, and especially to a hybrid drive unit having an engine and two motors or motor-generators.
Discussion of the Related Art
JP-A-2014-51146 describes one example of the hybrid drive unit of this kind. According to the teachings of JP-A-2014-51146, an engine and a first motor for controlling an engine speed are connected to rotary elements of a first planetary gear unit serving as a power distribution device, and a second planetary gear unit serving as a transmission for changing torque of an output element of the first planetary gear unit is connected to the first planetary gear unit. The second planetary gear unit comprises an input element connected to the output element of the first planetary gear unit, a reaction element, an output element, a first engagement device selectively halting the reaction element, and a second engagement device selectively integrating the second planetary unit by connecting the reaction element with the input element.
In the hybrid vehicle having the power distribution device, the engine may be cranked by the first motor connected thereto. A torque of the motor for cranking the engine may be increased by a torque increasing device taught by Japanese Patent No. 3852321.
Japanese Patent No. 5391959 also describes the drive unit for a hybrid vehicle in which a transmission is placed on an output side of a power distribution device. According to the teachings of Japanese Patent No. 5391959, a planetary gear unit serving as a transmission comprises a fixed sun gear, a carrier as an input element, and a ring gear as an output element, a first clutch for connecting the ring gear with an output gear, a second clutch for connecting the carrier with the output gear, and a brake for halting the carrier. In the hybrid vehicle taught by Japanese Patent No. 5391959, an operating mode may be selected from EV mode in which the vehicle is powered by a second motor, a series mode in which the vehicle is powered by the second motor driven by an electric power generated by driving a first motor by the engine, and hybrid mode in which an engine torque is distributed to the first motor and to the output gear, and in which the vehicle is powered by torques of the output gear and the second motor.
In the hybrid drive unit taught by JP-A-2014-51146, the output element of the power distribution device is thus connected to the transmission adapted to shift a gear stage between a high stage and a low stage so that a drive torque or an output speed can be changed depending on the gear stage. In the hybrid drive unit of this kind, the first motor has to establish a reaction torque during generating the engine power and hence cannot be used to generate a torque for propelling the vehicle. That is, according to the teachings of JP-A-2014-51146, the vehicle cannot be powered by the engine and the first and the second motors simultaneously. Such operating mode to power the vehicle by all of the prime movers is also not available in the hybrid drive units taught by Japanese Patent Nos. 3852321 and 5391959.